1. Technical Field
The present invention relates to a liquid discharge device and a head unit.
2. Related Art
As an ink jet printer that prints images and texts by discharging ink, a printer that uses piezoelectric elements is known. The piezoelectric element is provided corresponding to each of a plurality of nozzles in a head unit. Each piezoelectric element is driven according to a drive signal, so that a predetermined amount of ink (liquid) is discharged from a nozzle at a predetermined timing, and a dot is formed. The piezoelectric element is a capacitive load such as a capacitor from an electrical point of view, so that a sufficient amount of current has to be supplied to drive the piezoelectric element of each nozzle.
Therefore, a drive signal amplified by an amplifier circuit is supplied to the head unit to drive the piezoelectric element. As the amplifier circuit, there is a method where a source signal before amplification is amplified by a class AB amplifier. However, this method is not energy-efficient. Therefore, in recent years, a method using a class D amplifier is proposed (see JP-A-2010-114711). To put it plainly, the class D amplifier amplifies an input signal by performing pulse width modulation and/or pulse density modulation on a source signal, switching a high side transistor and a low side transistor serially inserted between power supply voltages according to the modulation signal, and demodulating an output signal generated from the switching by using a low pass filter (a demodulator) including an inductor (a coil) and a capacitor.
To cause a piezoelectric element to discharge ink by a drive signal amplified by the class D amplifier, it is necessary to raise the frequency of the modulation signal to some extent. However, a problem is pointed out where, when switching the high side transistor and the low side transistor according to a modulation signal of a relatively high frequency, an operation becomes unstable due to effects of noise and the like.